The manufacture of insulation products based on mineral wool generally comprises a step of manufacture of the wool itself, which can be carried out by various methods, for example according to the known technique of fibre production by internal or external centrifugation.
Internal centrifugation consists of introducing the molten mineral material (glass or rock) into a centrifuge comprising a multitude of small orifices, the material being projected towards the peripheral wall of the device under the action of centrifugal force and leaving it in the form of filaments. At the outlet of the centrifuge, the filaments are stretched and entrained towards a receiving device by a high-temperature and high-velocity gas stream, forming a layer of fibres (or mineral wool).
External centrifugation involves pouring the molten material onto the external peripheral surface of rotating parts called rotors, from where the molten material is ejected under the action of centrifugal force. Means are also provided for stretching by a gas stream and for collecting on a receiver.
To ensure that the fibres are gathered together and to provide the layer with cohesion, a bonding composition containing a thermosetting resin is sprayed onto the fibres, on its path from the centrifuge outlet to the receiving device. The layer of fibres coated with the binder is submitted to a thermal treatment, at a temperature generally above 100° C., in order to effect polycondensation of the resin and thus obtain a thermal and/or acoustic insulation product having specific properties, notably dimensional stability, tensile strength, recovery of thickness after compression and uniform colour.
The bonding composition that is to be applied on the mineral wool is generally in the form of an aqueous solution containing the thermosetting resin and additives such as a crosslinking catalyst for the resin, an adhesion-promoting silane, an anti-dust mineral oil, etc. The bonding composition is generally applied on the fibres by spraying.
The properties of the bonding composition largely depend on the characteristics of the resin. From the standpoint of application, the bonding composition must have good sprayability and must be able to be deposited on the surface of the fibres so as to bind them effectively.
The resin must be stable for a given period of time before it is used for forming the bonding composition, said composition generally being prepared at the moment of use by mixing the resin and the additives mentioned above.
In regulatory terms, the resin must be non-polluting, i.e. it should contain—and should generate during the bonding step or subsequently—the minimum possible amount of compounds that can be harmful to human health or to the environment.
The thermosetting resins most commonly used are phenolic resins of the resol class. Besides their good crosslinking capacity in the aforementioned thermal conditions, these resins are water-soluble, possess good affinity for mineral fibres, notably of glass, and are relatively inexpensive.
The commonest resols are obtained by condensation of phenol and formaldehyde, in the presence of a basic catalyst. At the end, these resols contain a certain proportion of unreacted monomers, in particular formaldehyde, whose presence is undesirable on account of its known harmful effects.
For this reason, resol-based resins are generally treated with urea, which reacts with the free formaldehyde, trapping it in the form of non-volatile urea-formaldehyde condensates. Moreover, the presence of urea in the resin gives a certain economic advantage owing to its low cost, as it can be introduced in relatively large amounts without affecting the usage qualities of the resin, notably without adversely affecting the mechanical properties of the finished product, which lowers the total cost of the resin considerably.
It has nevertheless been observed that, in the temperature conditions to which the layer is subjected to obtain crosslinking of the resin, urea-formaldehyde condensates are unstable; they decompose giving formaldehyde and urea again, the latter being degraded at least partially to ammonia, and they are released into the workshop atmosphere.
Regulations on environmental protection have become stricter and they oblige manufacturers of insulation products to find solutions by which the levels of undesirable emissions, especially of formaldehyde, can be reduced even further.
Solutions for replacing resols in the bonding compositions are known and are based on the use of a carboxylic acid and an alcohol.
In U.S. Pat. No. 5,340,868, the binder comprises a polycarboxylic polymer, a β-hydroxylamide and an at least trifunctional monomeric carboxylic acid.
Bonding compositions have also been described comprising an alkanolamine containing at least two hydroxyl groups and a polycarboxylic polymer (U.S. Pat. No. 6,071,994, U.S. Pat. No. 6,099,773, U.S. Pat. No. 6,146,746) which can be combined with a copolymer (U.S. Pat. No. 6,299,936).
Bonding compositions comprising a polycarboxylic polymer and a polyol have also been proposed (US 2002/0091185, US 2002/0091185). These compositions can in addition contain a catalyst, which can be a compound containing phosphorus (U.S. Pat. No. 5,318,990, U.S. Pat. No. 5,661,213, U.S. Pat. No. 6,331,350, US 2003/0008978), a fluoroborate (U.S. Pat. No. 5,977,232) or a cyanamide, a dicyanamide or a cyanoguanidine (U.S. Pat. No. 5,932,689), or a cationic, amphoteric or non-ionic surfactant (US 2002/0188055), or a coupling agent of the silane type (US 2004/0002567).
WO 2006/120523 describes a bonding composition which comprises (a) a poly(vinyl alcohol), (b) a multifunctional crosslinking agent selected from non-polymeric polyacids or salts thereof, anhydrides or a non-polymeric polyaldehyde and (c) optionally a catalyst, the (a)/(b) weight ratio being in the range from 95:5 to 35:65 and the pH being at least equal to 1.25.
From WO 2008/053332, a bonding composition is also known which comprises an adduct of (a) a sugar polymer and (b) a multifunctional crosslinking agent selected from monomeric polyacids or salts thereof, and anhydrides, which is obtained in conditions such that the (a)/(b) weight ratio is in the range from 95:5 to 35:65.
Moreover, bonding compositions have been described in which all or part of the alcohol is replaced with one or more saccharides.
In US 2005/0215153, the bonding composition is formed from a pre-binder containing a polymer of carboxylic acid and of a polyol, and a dextrin as co-binder.
In U.S. Pat. No. 5,895,804, the bonding composition comprises a polycarboxylic polymer with a molecular weight of at least 1000 and a polysaccharide with a molecular weight of at least 10 000.
In WO 2009/080938, the bonding composition comprises at least one organic polycarboxylic acid of molecular weight less than or equal to 1000 and at least one monosaccharide and/or polysaccharide.
Finally, a bonding composition is known from WO 2010/029266 that comprises at least one hydrogenated sugar and a polyfunctional crosslinking agent.